Prior attempts to achieve acceptable flame-resistant nylon/cotton blends have not met with commercial success. None of the treatments are practical from the consumer point of view, producing fabrics that have a very stiff hand. This is because in order to achieve the requisite flame-resistant properties, a high chemical add-on is required. This add-on makes the fabric stiff, masks the color of the underlying fabric, and often imparts an acrid or unacceptable odor to the fabric. In addition, the performance of the flame resistant fabrics is often unreliable.
Acceptable flame resistance has been obtained on nylon/cotton blends by use of White Chemical Company's finish "Caliban P-44", which employs a high add-on of decabromobiphenyl oxide and antimony oxide. However, this flame retardant is held on the fabric by a substantial quantity of latex binder, and the finished fabric has an unacceptably stiff, rubbery hand and seriously altered appearance.
Most of the previous work conducted on flame-resistant nylon/cotton blends used a single chemical system that was targeted for the cotton component of the blend. The approach was to "load" the fabrics with a flame retardant specific for cotton, for instance THPS [tetrakis-(hydroxymethyl)phosphonium sulfate]. It was not unusual with these earlier products to use from 30 to 35% of fixed chemical add-on in order for the nylon/cotton blend fabric to pass a bottom vertical flame test. Regrettably, however, the aesthetics of the finished fabrics were poor, as they had a very stiff hand and the appearance of a coated fabric. The add-ons used for these products were far in excess of the theoretically required amounts.
When THPS is applied to a nylon/cotton blend, about 1.7% of fixed phosphorus is required to achieve flame resistance. The use of this quantity of reagent typically results in a stiff fabric with unacceptable hand. An object of the present invention is to produce acceptable flame-resistant nylon/cotton blends using multiple flame-retardant chemicals or chemical systems, and to employ processing conditions or adjuvants that produce a commercially acceptable, attractive product having good color and acceptable hand.
Disclosed is a process for imparting flame-resistant properties to a nylon/cotton blend fabric, usually containing from at least 15 weight percent up to 55 or 60 weight percent nylon, by applying either separately or simultaneously, a flame retarding amount of (a) a cyclic phosphonate ester flame retardant that fixes onto the nylon fibers and (b) a flame retarding amount of a tetrakis-(hydroxymethyl)phosphonium salt/urea polymer that fixes onto and into the fibers of the cotton fibers. The flame retardants are applied to the fabric, either separately or together, conveniently by padding, then the coated fabric is heated to cure the polymer and fix both flame retardants on to the nylon and cotton fibers, respectively.